ABSTRACT
The optical activity of organic compounds produced by living cells is still a mystery more than 170 years after Louis Pasteur discovered it as the best borderline between the chemistry of inanimate and living matter. Initial nonequilibrium conditions were probably the prerequisite for the origin of homochirality and life. We are not sure if the abiotic origin for the protonmotive force can explain both. However, intermittent and insecure free-energy inputs are not enough to jump-start the development of terrestrial or deep-ocean life hatcheries in geochemical environments rich with minerals and simple organic molecules. “Chemical bags” proposals devoid of membrane-based bioenergetics are no longer plausible. Other life-origin ideas include RNA-world-first, lipid-world first, metabolism-first, and bioenergetics-first proposals. Already in the Hadean era, about four billion years ago, the geochemistry could have obtained the vectorial character that is the characteristic of biochemistry. Not anywhere, of course, but the catalytic labyrinth of thin mineral membranes, separating cold ocean water from hot alkaline venting fluids, could have existed at multiple ocean-floor sites before life appeared. It probably maintained the required gradients of temperature, pH, inorganic, and simpler carbon compounds. The H2 and CO2 molecules were plentiful in diverse geochemical environments of the Hadean era. The carbon fixation (methane synthesis) was an easy solution for the faster dissipation of far-from-equilibrium gradients. There is some congruence between present-day metabolism with a central role for pyruvate and possible abiotic enzyme-less synthesis of pyruvate under conditions prevailing in Hadean and Archaean geochemical reactors. The yield of amino acids, sugars, nucleotides, and simpler lipids was initially low but quickly increased once a set of autocatalytic reactions was established. The “dissipation-first” hypothesis for the origin of life shifts the research-focus from the efficiency of building up organic molecules to the efficiency of consuming available thermodynamic gradients. Integration to a hierarchical organization is an efficient mechanism for funneling flows through the steepest descents in the free energy landscape for both inanimate and animate systems. Thus, order-promoting dissipation must have been tightly coupled with the origin of life.
